How to make a knight helmet face?
Here's one approach:

Create a mesh circle with 8 points in the side view:



Scale it to get the profile you want:



Delete all but the bottom corner of it:



Go to the top view and make an 8 point cylinder and align it with the circle from the side view:



Then go back to the side view and scale it so that it matches your quarter circle mesh:



Subdivide the vertical edges and then drag the points to the right and down to match your profile:



Go to the top view and delete the edges on the left half:



Delete the back faces:



Select the vertices in the back and snap them even with the right side:



Add a Mirror modifier:



Grab the middle vertices and pull them downwards:



Select the edges to the right of the middle:



Subdivide them:



Select the new edge and do Edge Slide to move them right up next to the middle edge:



Add a Subdivision modifier, and you can see we've got that pointed crease in the middle:



If you then go to the front view and pull up the middle verts a bit:



Then go to the side and delete these faces:



Select the upper row of edges:



Subdivide:



Select the new edge and Edge Slide it up near the top edge:



And that's got you pretty far along on the top visor already:



You can do the bottom similarly, but it's almost straight, so you wouldn't need as many edges.  Just make another cylinder in top view, cut it in half, mirror it, and move the edges where you want them.





I hope that's enough to get you going.  Sorry if it's too much detail as I don't know your modeling skill level.  Good luck!